The purpose of this contract is to establish and maintain a cryopreserved embryo bank of genetically defined laboratory rats and mice derived from the NIA colonies of aged rats and mice, which can be used to re-establish any particular strain should a genetic contamination or deviation be detected after rederivation of the NIA colonies, or a disease or environmental disaster occur. Similarly, should an investigator's results start deviating from their past norm after one or more rederivations have occurred, embryos from this stock would be used to try and determine if the evolution of effects seen was of animal or investigator origin. Prior to the cessation of entry of animals into each of the three currently established NIA aging rodent colonies, breeder males and females or pregnant female foundation stock will be sent to the Contractor for expansion to yield sufficient number of potential embryo donors.